In general, a Zener diode operates with a reverse bias when it is applied in a circuit. When a reverse bias voltage applied to a Zener diode exceeds a certain value, the current flowing through the diode rises rapidly due to the electron tunneling effect. This reverse voltage is referred to as the Zener breakdown voltage. The current flow in the forward direction of a Zener diode is similar to that of a traditional diode.
The basic structure of a Zener diode includes a p-n junction. The Zener breakdown voltage can be adjusted by selecting an appropriate doping material and concentration. Conventional Zener diodes include doping areas that have the shape of a rectangle. FIG. 1A shows a plan view of a conventional n-type base Zener diode 100. FIG. 1B shows a cross-sectional view along a section line AA illustrated in FIG. 1A. Zener diode 100 is formed in an n-type well region (N-Well or NW) 102 of a semiconductor substrate 104, and includes a p+ doped region 106, at least one n+ doped region 108, and at least one n-type base region (NBASE) 110. An anode 112 of diode 100 is coupled to p+ doped region 106, and at least one cathode electrode 114 is coupled to n+ doped region 108.
FIG. 2A shows a plan view of a conventional p-type base Zener diode 200. FIG. 2B shows a cross-sectional view along a section line AN as illustrated in FIG. 2A. Zener diode 200 is formed in a p-type well region (P-Well or PW) 202 of a semiconductor substrate 204 and includes an n+ doped region 206, at least one p+ doped region 208, and at least one p-type base region (PBASE) 210. A cathode 212 of diode 200 is coupled to n+ doped region 206, and at least one anode electrode 214 is coupled to p+ doped region 208.
As shown in FIGS. 1A, 1B, 2A, and 2B, conventional Zener diodes have doped regions, such as regions 106, 108, 206, and 208, in the shape of a rectangle. It has been proposed to increase the switching speed of Zener diodes so as to meet the demand for higher performance and to avoid circuit failure due to the slow switching behavior of the conventional Zener diodes.